ACCC chairman Rod Sims says he does not have a problem with such discounting; it was price distortion in the fuel market that was the watchdog's main concern.

Woolworths lost 1.4 per cent to $33.52 and the owner of Coles, Wesfarmers, lost 1.3 per cent to $42.39.

Shares in building products maker Boral fell 0.4 per cent to $4.70 despite the company saying favourable weather will help lift its first-half profit to around $90 million after a loss for the same period a year ago.